Better Odds That Life Crashed to Earth From Space
The researchers report in the journal Astrobiology that under certain conditions, there is a high probability that life came to Earth --or spread from Earth to other planets -- during the solar system's infancy when Earth and its planetary neighbors orbiting other stars would have been close enough to each other to exchange lots of solid material.
The findings provide the strongest support yet for "lithopanspermia," the idea that basic life forms are distributed throughout the universe via meteorite-like planetary fragments cast forth by disruptions such as planet and asteroid collisions. Eventually, another planetary system's gravity traps these roaming rocks, which can result in a mingling that transfers any living cargo.
"We wanted to know how debris left over from the formation of our solar system can get transported from one planetary system to another," said Renu Malhotra, a professor of planetary science in the UA's Lunar and Planetary Laboratory.
"Even today, some of these rocks leak out of the asteroid belt and hit planets," said Malhotra. "That's how we get meteorites. Some of them land on other planets, and some get thrown out of the solar system."
"With this study, we wanted to find out what happens to those small rocks that are thrown out and escape the solar system. Where do they go?"
Previous research suggested that, typically, those small rocks called meteoroids leave the solar system at high speeds, making the chances of being snagged in the gravitational pull of another object highly unlikely.
"Those studies assumed a typical velocity of 5,000 meters per second or more," said Malhotra. "They neglected the small fraction of material leaving a solar system at speeds slow enough to be captured by other planetary systems."
Using the star cluster in which our sun was born as a model, the team conducted simulations showing that at these lower speeds, the transfer of solid material from one star's planetary system to another could have been far more likely than previously thought, explained first author Edward Belbruno, a mathematician and visiting research collaborator in the department of astrophysical sciences at Princeton University who developed the principles of weak transfer.
Weak transfer describes a low-velocity process wherein solid materials meander out of the orbit of one large object and happen into the orbit of another. In this case, the researchers factored in velocities 50 times slower than previous estimates, or about 100 meters per second.
The researchers suggest that of all the boulders cast off from our solar system and its closest neighbor, five to 12 out of 10,000 could have been captured by the other. Earlier simulations had suggested chances as slim as one in a million.
"Our work says the opposite of most previous work," Belbruno said. "It says that lithopanspermia might have been very likely, and it may be the first paper to demonstrate that. If this mechanism is true, it has implications for life in the universe as a whole. This could have happened anywhere."
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